Save a copy of your return as filed, and then in the original file navigate to 1040X and select 2025 as the amendment year on the "amendment year smart worksheet". 

Then enter the deductible IRA contribution.

Finally, navigate to the Info Wks and scroll down to "Federal Amended or Superseded Returns" and check the box "File federal superseded return electronically".  This will ensure that you transmit a superseded rather than amended return - even though the process begins on the 1040X worksheet.